1. Field of the Invention
The present invention relates to a light-sensitive composition suitable for producing presensitized plates for use in making lithographic printing plates, print-circuit boards for IC or photomasks and more particularly to a light-sensitive composition which comprises a positive-working light-sensitive compound and a polymeric compound excellent in wear resistance.
2. Description of the Prior Art
Light-sensitive compositions comprising an o-quinonediazide compound and a novolak type phenolic resin have industrially been employed to produce a presensitized plate for use in making lithographic printing plates (hereunder referred to as "PS plate(s)" for simplicity) or as a photoresist because of very excellent properties thereof.
However, the novolak type phenol resins used as a principal ingredient for such a light-sensitive composition suffer from various kinds of disadvantages to be eliminated, such as low adherence to a substrate used, formation of a fragile film, low coating performance, low wear resistance and insufficient printing durability of the resulting lithographic printing plates when they are used for manufacturing PS plates. Therefore, the application thereof is restricted to a narrow range.
In order to solve the foregoing problems, it has been proposed to use a variety of polymeric compounds as a binder. For example, Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J. P. KOKOKU" No. 52-41050 discloses the use of polyhydroxystyrene or hydroxystyrene copolymer as such a binder. These polymers surely permit the improvement of coating performance of the resulting light-sensitive composition while the problem with respect to wear resistance thereof still remains unsolved. In addition, Japanese Patent Un-Examined Published Application (hereinafter referred to as "J. P. KOKAI") No. 51-34711 proposes the use of a polymeric compound having structural units of an acrylic acid derivative within the molecular structure thereof as a binder. However, the use of such a polymeric compound largely restricts the range of proper developing conditions and provides insufficient wear resistance.
On the other hand, polyurethane resins have been known as a polymer excellent in wear resistance and, for instance, J. P. KOKOKU No. 49-36961 discloses a light-sensitive composition which comprises a combination of a positive-working diazonium compound and a substantially linear polyurethane resin. However, the polyurethane resin does not include alkali-soluble groups and thus is essentially less soluble in an aqueous alkaline developer. This makes the development difficult and a part of the film to be removed remains undissolved.
Furthermore, J. P. KOKAI No. 61-20939 discloses a light-sensitive composition in which an anionic polyurethane resin is incorporated. However, the anionic polyurethane resin is water-soluble and, therefore, it has insufficient solubility in an organic solvent used for preparing a coating liquid. Moreover, the resin is not preferred since it impairs the stability of the diazo compounds.